1. Technical Field
The present invention relates generally to Cellular Digital Packet Data (CDPD) networks; and more particularly to a system and method of operation in which a mobile network location protocol (MNLP) operates to correctly route Location Update Service (LUS) messages within a CDPD network.
2. Related Art
A CDPD network is a wireless wide-area data network (WAN) that enhances the services provided by cellular carriers by supporting packet based data transfer operations. It is based on the Internet Protocol (IP) and is designed to minimize the impact on network software by requiring no changes to the higher network protocols. In its most basic form, a CDPD network can be used as a wireless extension of an existing TCP/IP network. It allows mobile workstations to talk to host computers to retrieve information such as stock inventory, dispatched messages, or location information. CDPD is the standard packet communications architecture for the North American cellular telecommunications industry and is currently being deployed in Canada, the United States and Mexico.
A CDPD network typically includes a plurality of Mobile Data Base Stations (MDBSs), a plurality of Mobile Data Intermediate Systems (MDISs), a network backbone, a Network Administrative Support System (NASS) and a Network Control Center (NCC). Together, the components of the CDPD network support communications with Mobile End Systems (MESs). The NASS and the NCC provide management functions for the CDPD network.
MESs allow subscribers of the CDPD network to gain access to wireless communications provided by the CDPD network. An MES can be any mobile computing device which has a CDPD modem installed or attached to it. An MES can support several types of features. For example, some MESs support CDPD access only and others have dual mode (circuit switched and CDPD) access. Some MESs provide integrated cellular voice and data capabilities along with PSTN connectivity.
The MDBS is Radio Frequency (RF) equipment that is located at a cell site that supports RF communications between an MES and an MDIS and manages communications across the radio channels. Each MDIS may support multiple MDBSs. The location of each MDBS is based on engineering analysis of coverage topology and data traffic loading predications, optimized for both off-peak and busy hour traffic conditions.
The MDIS is the central switching fabric for the CDPD network. The MDIS has primary responsibility for providing mobility management and packet routing to ensure data is exchanged with MESs as they traverse the various MDBSs comprising the network. The MDIS couples to the network backbone and passes all traffic via the network backbone. The network backbone is typically comprised of standard IP routers and networking equipment to support network management and security. The network backbone may couple to external data networks via a router. For example, the CDPD network may couple to the Internet, public and private packet switched networks and other networks that provide data transfer functions.
The CDPD network provides Network Layer services to applications riding over it. Applications riding upon the CDPD network include IP applications and Connectionless Network Protocol (CLNP) applications among others. The CDPD network is compatible with the well known International Standards Organization (ISO) Reference Model for Open Systems Interconnection. To support IP based applications and CLNP applications, among others, the CDPD network provides the Network Layer services transparently to the applications riding above the Network Layer. As compared to the non-mobile operations of IP networks, the CDPD services MESs that roam throughout the CDPD network, connecting to differing local MDBSs during such roaming.
The Mobility Network Location Protocol (MNLP) was developed to provide the Network Layer support in the CDPD network. The MNLP facilitates mobility within the CDPD network, locating MESs within the CDPD network and routing packet data to and from the MESs. Consistent with the MNLP, the Location Update Service (LUS) and the Forwarding Service (FS) provide Network Layer support within the CDPD to locate the MESs within the CDPD network and to deliver packet data to the MESs once their location is determined. However, the LUS and the FS are distinct services within the ISO Reference Model and must maintain their isolation from one another so as not to violate proper network protocol practice.
Each MES has an associated "Home" MDIS. All packet data intended for a particular MES supported by the CDPD network is routed to its Home MDIS. The Home MDIS then routes the packet data via the network backbone to a "Serving" MDIS that currently serves the MES. The Serving MDIS then routes the packet data via an appropriate MDBS to the MES. For packet data transmissions emanating from the MES, the Serving MDIS routes the packet data according to an associated destination address, but not necessarily via the Home MDIS.
As the MES moves about the CDPD network, the LUS is employed to notify the Home MDIS of the current Serving MDIS. For example, when an MES first operates within an area served by a particular MDIS, the MES attaches to an MDBS serviced by the MDIS. When the MES attaches to the MDBS, the Serving MDIS uses the LUS to send a ReDirect Request (RDR) to the Home MDIS which directs the Home MDIS to direct all further packet data to the Serving MDIS. Upon receipt, the Home MDIS updates its routing tables and sends a ReDirect Confirmation (RDC) to the Serving MDIS. Then, all subsequent packet data received by the Home MDIS intended for the MES is routed by a Forwarding Service (FS) to the Serving MDIS for delivery via a serviced MDBS.
However, during some operations, the LUS fails to properly register a redirection. When the RDR is routed via an "Intermediate" MDIS to the Home MDIS, the LUS loses the LUS address of the Serving MDIS. Such is the case because the RDR of the LUS only carries the FS address of the Serving MDIS, which oftentimes differs from the LUS address of the Serving MDIS. If the Home MDIS issues an RDC using the FS address of the Serving MDIS, the RDC may fail to reach the Serving MDIS. Resultantly, the CDPD network does not forward data intended for the MES to the Serving MDIS.
Thus, there is a need in the art for a system and an associated method of operation wherein the Home MDIS can properly identify the LUS address of the Serving MDIS when the LUS routes the RDR from the Serving MDIS to the Home MDIS via an Intermediate MDIS.